1. Field of the Invention
The present invention relates to a hydraulic brake apparatus for a vehicle, which is adapted to actuate a master piston by hydraulic braking pressure discharged from a hydraulic pressure source, in response to operation of a brake pedal, or irrespective of operation of the brake pedal.
2. Description of the Related Arts
In German Patent No. DE19542656A1, a hydraulic brake apparatus having a hydraulic pressure source in addition to a master cylinder is disclosed. In the patent, there is disclosed a technology for performing an automatic pressurization by applying hydraulic pressure of a pressure source to a back of a power piston which is integrally connected to a brake pedal. The pressure source includes a hydraulic pressure pump, accumulator or the like. The automatic pressurization is a control for generating the hydraulic braking pressure from the master cylinder so as to perform a traction control, vehicle stability control or the like, when the brake pedal is not operated.
According to the apparatus as disclosed in the above-described German Patent No. DE19542656A1, when the automatic pressurization is performed, the brake pedal is advanced, without being operated, by a stroke (Sto) of the brake pedal corresponding to the automatically pressurized amount, as indicated by a two-dotted chain line in FIG. 6. Therefore, when the brake pedal is operated in that state, i.e., when the brake pedal is depressed further, while the automatic pressurization is being performed, the brake pedal will be in such a state as to receive a reaction force of load (Of) which corresponds to the hydraulic braking pressure produced by the automatic pressurization with the position of the stroke (Sto) advanced. Thereafter, the pedal load (reaction force) is increased in response to increase of the stroke according to a strokexe2x80x94pedal load characteristic for a normal operation of the brake pedal. As a result, when the brake pedal is operated further, while the automatic pressurization is being performed, the starting position of the stroke is not placed at the position of the stroke (0), but placed at the position of the stroke (Sto), whereby a stroke stiffness is made so high that it will be difficult to advance the brake pedal.
Accordingly, it is an object of the present invention to provide a hydraulic brake apparatus having a power chamber formed behind a master piston, and supplied with power pressure by a power source to perform automatic pressurization, wherein a proper brake feeling can be obtained, even if the brake pedal is operated while the automatic pressurization is being performed.
In accomplishing the above and other objects, the hydraulic brake apparatus for a vehicle includes wheel brake cylinders operatively mounted on wheels of the vehicle, respectively, and a master cylinder for advancing a master piston in response to operation of a brake pedal to apply a hydraulic braking pressure to the wheel brake cylinders. A power chamber is formed behind the master piston. A reaction piston is disposed, with the front end thereof exposed in the power chamber, to transmit a reaction force produced by the pressure in the power chamber to the brake pedal. The apparatus further includes a reservoir for storing brake fluid, a power source for pressurizing the brake fluid stored in the reservoir to supply power pressure to the power chamber, a return passage for connecting the power chamber to the reservoir to return the brake fluid thereto, and a valve device for opening and closing the return passage. A detection device is provided for detecting the amount of operation of the brake pedal. And, a controller is provided for controlling the valve device to be opened and closed in response to the amount of operation of the brake pedal detected by the detection device to reduce the amount of the brake fluid in the power chamber. According to the apparatus as described above, therefore, even if the brake pedal is operated during the automatic pressurization, with the power pressure supplied by the power source, the brake fluid in the power chamber is reduced by controlling the valve device to be opened and closed, to obtain a sufficient stroke of the brake pedal, so that an adequate brake feeling can be obtained.
In the apparatus as described above, the controller is preferably adapted to control the valve device to increase the amount of brake fluid returned from the power chamber to the reservoir through the return passage, in response to increase of the amount of operation of the brake pedal detected by the detection device.
The controller may be adapted to control the valve device to control the amount of brake fluid returned from the power chamber to the reservoir through the return passage to be smaller than the amount of brake fluid discharged from the master cylinder in response to operation of the brake pedal.